The present invention relates to a transmission having a hydrodynamic drive with a special type of hydromechanical transmission. The hydrodynamic drive is mounted on the output of the hydromechanical transmission for operation under starting conditions only. Its purpose is to simplify the control at the start and to make the starting smooth, as well as to isolate the transmission from possible engine torsional vibration. The hydromechanical transmission is that described and claimed in my U.S. Pat. No. 3,888,139.
The present invention is a three-range transmission in which the hydrodynamic drive, such as a fluid coupling or a torque converter, operates between zero speed and the bottom of a low range when the low clutch is engaged, and does not operate thereafter. The shift between forward and reverse is preferably accomplished by mechanically shifting a dog clutch between two positions identified as "forward" and "reverse," because a torque converter is capable of multiplying the torque in one direction only; in the opposite direction, the torque converter runs as a fluid coupling without multiplying the torque.